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This SAE Recommended Practice is intended to apply to lamps, batteries, heaters, radios, and similar equipment for operation with mobile or automotive diesel engines. Twenty-four V systems have long been used for heavy-duty services because 24 V permit operating 12 V systems in series-parallel. Thirty-two V systems have been used for marine, railroad-car lighting, and other uses. Generators, storage batteries, starting motors, lighting, and auxiliary electrical equipment shall be for nominal system ratings of 12, 24, or 32 V as determined by the power requirements of the application. It is recommended that no intermediate voltages be considered. The combination of a 24 V starting motor and two 12 V batteries connected in series for cranking is considered practical where it can be adapted to the installation.

The electrical cranking system components, which include the battery, cables, and cranking motor, must be carefully selected to provide the necessary speed to start an engine under the most severe climatic conditions for which the system is intended. Engine cranking loads increase with cold temperatures, therefore, the initial selection of these components needs to consider low-temperature engine torque requirements. To insure an adequate electrical cranking system is obtained, it is important that proper test procedures are used for obtaining the cranking load requirements of the engine.